Effect of maturation conditions on light and temperature requirements during seed germination of Citrullus colocynthis from the Arabian Desert.

Seed germination of Citrullus colocynthis, as in many other species of Cucurbitaceae, is inhibited by light, particularly at low temperatures. Germination response to light and temperature has been attributed to day length and temperature during seed maturation. This study assessed the effects of these factors on the germination response of C. colocynthis to temperature and light quality. Ripe fruits were collected from natural habitats during December and February and germinated at three temperatures (15/25, 20/30 and 25/35 °C) in five light treatments (dark, white light and Red:Far Red (R:FR) ratios of 0.30, 0.87 and 1.19). Additionally, unripe fruits were also collected from natural habitats and completed their maturation in growth chambers under different day lengths (6, 16 and 24 h of darkness) at 10/20 °C, and in darkness at both 10/20 °C and 25/35 °C. Mature seeds of the different treatments were germinated in the same five light treatments at 15/25 °C. Germination was significantly higher in the dark than that in any light treatment. Seeds matured at higher temperatures (i.e. seeds from the December collection and those matured at 25/35 °C) had significantly higher germination than those matured at lower temperatures (i.e. seeds from the February collection and those matured at 10/20 °C). Dark germination was significantly higher for the December collection than for the February collection. Seeds of the two collections germinated in the dark only at 15/25 °C. However, seeds matured in a growth chamber at 10/20 °C in darkness germinated at 15/25 °C in all light treatments, except for the R:FR ratio 0.30. Seeds of the different treatments failed to germinate in FR-rich light. This study demonstrates that both temperature and day length during seed maturation play significant roles in the germination response of C. colocynthis. Additionally, the dark requirement for germination is likely beneficial for species with the larger seeds, such as C. colocynthis, which produce bigger seedlings that are able to emerge from deep soils and are competitively superior under dense vegetation and resource-limited conditions.

Large amounts of polylactic acid in contact with divided nerve sheaths have no adverse effects on regeneration.

The stumps of divided rat sciatic nerves were coapted by suturing the epineurium to a small rectangular device made of a sheet of polylactic acid. One month later, significant degradation of the implanted material was observed. At that time, the local condition of the nerve was excellent, and the precise location of the initial injury could not be determined by examination under the operating microscope. Histology confirmed that there was no visible reaction to the biodegradable substance or its metabolites, and that neurotization of the distal stump was satisfactory. These findings were in agreement with those of other studies, and indicated that polylactic-acid devices affixed to divided nerves have no adverse effect on regeneration.